LT1931 Linear Technology, LT1931 Datasheet

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LT1931

Manufacturer Part Number
LT1931
Description
1.2MHz/2.2MHz Inverting DC/DC Converters in ThinSOT
Manufacturer
Linear Technology
Datasheet

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FEATURES
TYPICAL APPLICATIO
APPLICATIO S
Fixed Frequency 1.2MHz/2.2MHz Operation
Very Low Noise: 1mV
– 5V at 350mA from 5V Input
–12V at 150mA from 5V Input
Uses Small Surface Mount Components
Wide Input Range: 2.6V to 16V
Low Shutdown Current: <1 A
Low V
Low Profile (1mm) ThinSOT
Pin-for-Pin Compatible with the LT1611
Disk Drive MR Head Bias
Digital Camera CCD Bias
LCD Bias
GaAs FET Bias
Local Low Noise/Low Impedance Negative Supply
V
5V
IN
CESAT
C1: TAIYO YUDEN X5R JMK212BJ475MG
C2: TAIYO YUDEN X5R LMK212BJ105MG
C3: TAIYO YUDEN X5R JMK325BJ226MM
D1: ON SEMICONDUCTOR MBR0520
L1: SUMIDA CLS62-100
Figure 1. 5V to –5V, 350mA Inverting DC/DC Converter
C1
4.7 F
Switch: 400mV at 1A
V
SHDN
IN
U
LT1931
10 H
GND
L1A
P-P
NFB
SW
Output Ripple
TM
Package
U
R1
29.4k
R2
10k
1 F
C2
C4
220pF
D1
10 H
L1B
DC/DC Converters in ThinSOT
1931 F01
C3
22 F
V
–5V
350mA
OUT
DESCRIPTIO
The LT
inverting SOT-23 current mode DC/DC converters. Both
parts include a 1A integrated switch allowing high current
outputs to be generated in a small footprint. The LT1931
switches at 1.2MHz while the LT1931A switches at 2.2MHz.
These high speeds enable the use of tiny, low cost
capacitors and inductors 2mm or less in height. The
LT1931 is capable of generating – 5V at 350mA or –12V
at 150mA from a 5V supply, while the LT1931A can
generate –5V at 300mA using significantly smaller induc-
tors. Both parts are easy pin-for-pin upgrades for higher
power LT1611 applications.
The LT1931/LT1931A operate in a dual inductor inverting
topology that filters both the input side and output side
current. Very low output voltage ripple approaching 1mV
can be achieved when ceramic output capacitors are used.
Fixed frequency switching ensures a clean output free
from low frequency noise typically present with charge
pump solutions. The low impedance output remains within
1% of nominal during large load steps. The 36V switch
allows V
The LT1931/LT1931A are available in the 5-lead ThinSOT
package.
ThinSOT is a trademark of Linear Technology Corporation.
, LTC and LT are registered trademarks of Linear Technology Corporation.
1.2MHz/2.2MHz Inverting
®
1931/LT1931A are the industry’s highest power
IN
to V
OUT
100
95
90
85
80
75
70
65
60
55
50
0
differential of up to 34V.
U
50
100
LOAD CURRENT (mA)
LT1931/LT1931A
Efficiency
150
200
250
300
1931 TA01
350
1
P-P

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LT1931 Summary of contents

Page 1

... LT1931A switches at 2.2MHz. These high speeds enable the use of tiny, low cost capacitors and inductors 2mm or less in height. The LT1931 is capable of generating – 350mA or –12V at 150mA from a 5V supply, while the LT1931A can generate –5V at 300mA using significantly smaller induc- tors ...

Page 2

... SHDN Pin Bias Current V SHDN V SHDN Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LT1931E/LT1931AE are guaranteed to meet performance specifications from Specifications over the – PACKAGE/ORDER I FOR ATIO SW 1 GND 2 ...

Page 3

... LT1931A –10 100 SHDN PIN VOLTAGE (V) 1931 G02 Oscillator Frequency 2.5 2.3 LT1931A 2.1 1.9 1.7 1.5 1.3 1.1 0.9 0.7 0.5 –50 – 1.2 TEMPERATURE ( C) 1931 G05 | V | – 255 OUT 255 . – • LT1931 5 6 1931 G03 LT1931 75 100 1931 G06 3 ...

Page 4

... SR latch is reset regardless of the state of comparator A2. This current limit protects the power switch as well as various external components connected to the LT1931. ) and m The Block Diagram for the LT1931A is identical except that the oscillator is 2.2MHz and resistors are one-half the LT1931 values. 1 COMPARATOR – ...

Page 5

... A 4 coupled inductor uncoupled inductor will usually be the best choice for most LT1931 designs. For the LT1931A 4.7 H coupled inductor uncoupled inductor will usually suffice. In certain applications such as the “Charge Pump” inverting DC/DC converter, only a single inductor is used ...

Page 6

... X7R, as these materials retain their capacitance over wide voltage and temperature ranges output capacitor is sufficient for most LT1931 applications while a 4 capacitor will suffice for the LT1931A. Solid tantalum or OS-CON capacitors can be used, but they will occupy more board area than a ceramic and will have a higher ESR ...

Page 7

... C1: TAIYO YUDEN X5R JMK212BJ475MG C2: TAIYO YUDEN X5R LMK212BJ105MG C3: TAIYO YUDEN XR5 JMK325BJ226MM OUT D1: ON SEMICONDUCTOR MBR0520 L1: SUMIDA CLS62-100 and C at SHDN Pin Provide Soft-Start to LT1931 Inverting Converter SS LT1931/LT1931A 500 s/DIV 1931 F06 Reaches – OUT = 15k and C = 33nF. Input current, measured ...

Page 8

... W U DIODE SELECTION A Schottky diode is recommended for use with the LT1931/ LT1931A. The Motorola MBR0520 is a very good choice. Where the input to output voltage differential exceeds 20V, use the MBR0530 (a 30V diode). These diodes are rated to handle an average forward current of 0 applications ...

Page 9

... SHDN R1 220pF LT1931 29.4k C1 4.7 F NFB GND R2 10k L2 4 OUT –5V 300mA C4 180pF C3 4.7 F 1931 TA05a LT1931/LT1931A Efficiency 100 100 125 150 50 LOAD CURRENT (mA) 1931 TA03 OUT –5V 300mA ...

Page 10

... 3 OUT –5V 200mA C4 68pF C3 4 10k 1931 TA06a LT1931 SHDN NFB GND 25. 68nF C6 R4 1000pF 2.7k *TOTAL OUTPUT POWER NOT TO EXCEED 3. C5: X5R OR X7R D1, D2: BAV99 OR EQUIVALENT L1: SUMIDA CR43-220 Efficiency ...

Page 11

... MAX) .00 – .15 .01 – .10 A1 (.00 – .006) (.0004 – .004) .90 – 1.30 .80 – .90 A2 (.035 – .051) (.031 – .035) .35 – .55 .30 – .50 REF L (.014 – .021) (.012 – .019 REF) LT1931/LT1931A 35V COM C5 4 25V V OUT1 –21.6V 48mA* ...

Page 12

... Linear Technology Corporation 12 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 www.linear-tech.com C2 L1A 0 SHDN R1 LT1931A 28.7k C1 2.2 F NFB GND R2 10k C1: TAIYO YUDEN Y5V EMK212F225ZG C2: 0.1 F 25V X5R C3: TAIYO YUDEN X5R JMK212BJ475MG D1: ON SEMICONDUCTOR MBR0520 L1: SUMIDA CLQ4D10-4R7 DRAWING #5382-T039 Efficiency ...

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